I know there are a variety of two level cooking rigs out there for the Egg, but I don't have one. I wanted to cook a couple briskets (~14lbs each) for a party and the Large BGE is my only cooker right now, so I decided to stack em. Bottom brisket went flat down and top brisket went flat up so I could get a good crust. I flipped them a couple times during the cook.
I was worried about the large mass of meat where the fat caps laid together sitting in a danger zone temp for too long. So I made sure to let the briskets come to room temp before putting on the cooker. Also, I started things at 300* and after a few hours when I had the meats at about 140* I turned down to 225* and went to bed. Came out real good!